they don't need a 55 gallon. Do you have any experience with them? Rainbows are less aggressive than red tails. and rainbows dont usually get 6 inches. usually around 4.5 or 5. just because you do a 5 minuet research on google and like 3 sites say they can be kept in 55 gallon+ does not mean that it is true. the majority of the sites say 29 gallon min. even if its a really trusted site, i'v found MAJOR problems. like putting a freaking Oscar in a 45 gallon. Point being, they are fine in a 30 gallon tank.